LeetCode 171 Excel Sheet Column Number

int titleToNumber(char* s) {
    int num = 0;
    char c;
    while(c = *s++)
    {
        num = num*26 + c - ‘A‘ + 1;
    }
    return num;
}

class Solution {
public:
    int titleToNumber(string s) {
        int ret = 0;
        for(int i = 0; i < s.size(); i ++)
            ret = ret*26 + (s[i]-‘A‘+1);
        return ret;
    }
};